1. Field
The invention relates generally to magnetic tape storage devices and systems, and more particularly to methods and systems for detecting and compensating for errors in a head position servo system of a magnetic tape storage drive.
2. Related Art
Increased data storage capacity, and retrieval performance, is desired of all commercially viable mass storage devices and media. In the case of linear tape recording a popular trend is toward multi-head, multi-channel fixed head structures with narrowed recording gaps and data track widths so that many linear data tracks may be achieved on a tape medium of a predetermined width, such as one-half inch width tape. To increase the storage density for a given cartridge size the bits on the tape may be written to smaller areas and on a plurality of parallel longitudinal tracks. As more data tracks are recorded on a tape, each track becomes increasingly narrow. The tape therefore becomes more susceptible to errors caused from the tape shifting up or down (called lateral tape motion or “LTM”) in a direction perpendicular to the tape travel path as the tape passes by the magnetic head.
Various servo techniques for tracking data tracks despite LTM are known, thereby increasing the track density and data storage capacity for a given size storage device. For example, recording servo information on the tape to provide positioning information to a tape drive system during writing and/or reading processes. Some systems include a magnetic or optical track of servo information which is detected and used as a position reference signal. For example, a variety of techniques have been used including dedicated and embedded magnetic servo tracks, time and amplitude magnetic servo tracks, optical servo tracks, tape edge detection, and the like. Other systems may intersperse or embed servo information with user data.
Such traditional servo techniques, however, may have errors associated therewith that limit the precision of the servo systems. For example, an optical servo system may include a detector for detecting the position of optically detectable indicia (e.g., dots or servo marks) associated with the storage medium. Errors, including non-linear errors, may result from a mismatch of an optical laser “spot” to the optically detectable indicia on the tape. Such errors may limit how narrow and dense tracks may be positioned for a given servo system.